The invention relates to magnetic resonance imaging (MRI) systems, particularly MRI systems for imaging breasts.
MRI systems typically employ a main magnet that produces a static magnetic field and gradient coils that superimpose spatially varying magnetic fields on top of the static field. The gradient coils are typically formed on a cylindrical insert that fits within the bore of the main magnet. Inside of the gradient coil insert there are RF transmitting and RF receiving coils (sometimes the same coil). The RF transmitting coil excites the molecules of the anatomy being imaged, and the RF receiving coil detects the response of the molecules.
MRI images can be used to guide biopsy and surgical tools. The anatomy of interest is imaged with one or more reference (“fiducial”) markers appearing in the image (or series of images). The surgical tool is installed in a known relationship to the reference markers (e.g., in a rotatable tool holder), and the tool is positioned so that upon insertion it will reach the lesion or other target found in the image (e.g., the tool holder is adjusted so that the target is at the center of rotation of the holder). Knowing the locations of the reference marker and the lesion makes IT possible to determine the position and orientation that the tool should be in for it to reach the target when inserted.
Often, the biopsy or surgical procedure is done after the patient is withdrawn from the MRI system, but the anatomy of interest is typically held stationary between the time that the images are taken and the surgery is completed.
This technique has been applied to some degree in biopsy of breast lesions. For example, in Schneider U.S. Pat. No. 5,855,554, MRI-transparent breast stabilization plates hold the breasts stationary, and reference markers built into the plates provide information for orienting the biopsy tool.